A guide to net carbs on keto

From the desk of
Luis Villaseñor
ScienceA guide to net carbs on keto

The central premise of the keto diet is simple: limit your carbohydrate intake to the point that your body prefers to use fat (and the ketones produced by metabolizing fat) as a primary source of energy.

For the average person, this usually means 50 grams or fewer net carbs per day. Yes, people bat an eye when I say that. But the key word is net. You see, not all carbs are created equal and therefore not all carbs need to be limited.

Specifically, fiber and sugar alcohols don’t significantly interfere with your ketogenic diet. Most fiber passes through the body undigested, and most sugar alcohols feed gut bacteria in your large intestine. Neither are converted to glucose for energy.

That’s why net carbs — which don’t include fiber and most sugar alcohols — are the only carbs that count toward your carb intake limit. This leaves a lot of room for veggies (and even some fruit!), depending on which ones you incorporate in your diet.

Unfortunately, most food labels and nutrition databases don’t report net carbs. They report total carbs. Oftentimes, 30 grams of net carbs can appear as 60-80 grams of total carbs. So if you rely on total carbs to navigate your keto diet, you’ll miss out on many fibrous keto-friendly foods, vitamins, and minerals. For example, an avocado has 11.6 grams of carbs but only 2.5 grams of net carbs count toward your daily tally. Similar arithmetic applies to green beans, broccoli, kale, zucchini, chayote, cauliflower and many other fiber-rich vegetables. These are important foods for hitting your micronutrient goals.

This article is a guide to net carbs on keto: how to calculate them, how to track them, why fiber doesn’t “count,” and the benefits of tracking net carbs vs. total carbs. Let’s get rolling.

Keto and Carb Restriction

Before covering net carbs, I want to explain why keto limits carbs.

Keto limits carbs because a low carb intake depletes the glycogen (stored glucose) in your liver. When your glycogen stores run low, your body believes it’s low on fuel and releases body fat for auxiliary power. In addition, low-carb diets keep blood sugar and insulin levels low. Low insulin, in turn, signals the release and breakdown of stored body fat — a process called lipolysis.

Once you have fatty acids floating around in your blood, they travel to your liver to be:

  1. Burned for energy (through a process called beta oxidation)
  2. Used to make ketones (through a process called ketogenesis)

As ketone levels rise, you enter a metabolic state called ketosis. In ketosis, you’re running primarily on fat and ketones produced from the breakdown of fatty acids for energy, rather than glucose. This can lead to benefits like better energy, sharper cognition, reduced cravings and less overeating. And assuming you’re in a caloric deficit, you get fat loss too!

This metabolic shift from carbohydrates to fat is only possible through carb restriction — if you have carbs available, your brain will use them first and foremost. Of course, other macros matter too (especially protein), but limiting net carbs to about 50 grams per day is the starting point. It kick-starts your backup metabolic machinery.

What are Net Carbs?

Net carbs are carbohydrates that have a metabolic impact. They contribute calories, and can raise your blood sugar and insulin levels enough to kick you out of ketosis.

Net carbs can be split into three categories:

  1. Simple carbs like fructose, glucose, and maltose
  2. Complex carbs like cellobiose and dextrin (think: apples)
  3. Starches (chains of glucose) from pasta, wheat, and potatoes

Unlike net carbs — which are absorbed through the small intestine and sent to the bloodstream to raise blood sugar — fiber and sugar alcohols buy a one-way ticket to the large intestine. Once they get there, they’re either fed to gut bacteria (via fermentation) or pass straight on through. Thus, dietary fiber and sugar alcohols have minimal calories and blood sugar effects.

So despite fiber and sugar alcohols appearing as carbs on food labels, they don’t count toward your net carb limit because they aren’t digested like other carbs. Here’s an neat equation to help you calculate net carbs instead of relying on total carbs:

Net carbs = total carbs – fiber – ½ sugar alcohols

  • Fiber. The main class of fiber that nourishes gut bacteria is called soluble fiber. Insoluble fiber can also fuel gut bacteria, but its primary function is to give form to stool. Neither contains calories. To illustrate with a few examples: Green vegetables that grow above ground are often rich in fiber and low in net carbs. On the other hand, roots such as onion, garlic, potato, yuka, and carrots are low in fiber, so they’re mostly net carbs. The same goes for foods like pasta, potatoes, apples, and whole grains: They’re mostly net carbs.
  • Sugar alcohols. Most sugar alcohols (like xylitol, sorbitol, and maltitol) are also fermented by gut bacteria, but after that they’re treated as regular carbohydrates. And while they’re less impactful than most other carbs, they still have calories and glycemic effects. For example, maltitol’s glycemic index (35) is significant, at about half that of table sugar (65). That means it will still raise blood sugar and insulin levels. In the equation above, I cut sugar alcohols in half before subtracting them from the total reported carbs — a slight simplification, but it works.

This equation lets you back into net carbs by subtracting out the carbs that don’t count. But why go to all this work? I’m glad you asked.

Advantages of Using Net Carbs vs. Total Carbs

There are three main reasons why calculating net carbs is worth your time:

#1: More dietary flexibility

All plant matter contains carbs as sugar, starch, or fiber. So when you significantly restrict your carbohydrate intake, you may lose access to many food groups. Paying attention to net carbs will help you be less restrictive with your food choices. You can include a wide variety of fibrous vegetables, and even a few fruits like blueberries, raspberries, and avocados.

These aren’t just benefits for your health, but also for your sanity. A keto diet that allows fiber is more enjoyable and more sustainable. It provides enough variety to keep your taste buds happy.

This doesn’t mean that a carnivore-style keto diet (with close to 0 total carbs) has no place. Many people with gut issues, for instance, report feeling their best on a diet of meat, water, and salt. But for most people, more flexibility is a good thing. And minding net carbs add a bit of flex.

#2: More micronutrients

Fiber-rich plants are some of the most nutrient-dense foods on the planet. For example, a typical serving of broccoli (1 cup) contains 6 grams of carbs, 3 of which are fiber. One cup of broccoli also contains:

  • 245% of your daily vitamin K (for blood clotting)
  • 135% of your daily vitamin C (for immune support and collagen production)
  • 42% of your daily folate (for energy production and DNA repair)
  • 19% of your daily vitamin B5 and 18% of your daily vitamin B6 (for energy production)
  • And many other vitamins and minerals

Broccoli also contains compounds called isothiocyanates that are being researched extensively for their health benefits. One isothiocyanate called sulforaphane, for instance, shows promising anticancer and anti-dementia properties.

And that’s just broccoli! Other plants have similarly robust profiles, and it’s hard to get enough micronutrients when you’re relying on total carbs to navigate your diet.

#3: More fiber

This is probably obvious by now, but using total carbs instead of net carbs will make you miss out on a lot of fiber too. Dietary fiber is important to keep digestion running smoothly and to feed your gut microbiome.

You may think of gut bacteria as mere passengers, but they’re an essential part of our biology. The gut microbiome influences heart health, skin health, brain health, oral health, and any other aspect of health that you can name. Fiber is what feeds that microbiome, helping to produce anti-inflammatory compounds like butyrate. Butyrate fuels colonic cells and may protect against colon cancer.

Higher fiber intakes have also been linked to heart disease prevention. In one meta-analysis, people consuming the most fiber (vs. those consuming the least) had about a 20% lower chance of dying from heart disease. Using net carbs brings more fiber into a low-carb diet. We like that!

How To Track Net Carbs

If you enjoy tracking your intake manually, feel free to use this equation with every food you eat:

Net carbs = total carbs – fiber – ½ sugar alcohols

But if you’re like me, you may want to automate this process. That’s what macro tracking apps are for! You have many options, but I like an app called Cronometer — it doesn’t just track your macronutrients, it also tracks net carbs and micronutrients.

You can see if you’re low on, say, potassium, and then adjust your diet and supplement routine accordingly. You don’t need to track net carbs forever, either. Getting a sense for your typical meals can make eating more intuitive and less calculated.

Plus, stick to these few rules, and you can pretty much forget about tracking carbs entirely:

  1. Eat mostly unprocessed foods
  2. Use your carb allowance for green-ish vegetables that grow above ground, and some low fructose fruit like blueberries or avocados
  3. Avoid sugar alcohols for simplicity

When you follow the rules above, it’s pretty difficult to eat more than 50 grams of net carbs in a day. Plus, you’ll get the added benefit of maximizing nutrient density. Log your meals for a few days, get a feel for it, and go on autopilot. Then you can just relax and enjoy the veggies!

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